21009420 has 36 divisors (see below), whose sum is σ = 63729120. Its totient is φ = 5602464.

The previous prime is 21009407. The next prime is 21009449. The reversal of 21009420 is 2490012.

It is a tau number, because it is divible by the number of its divisors (36).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21009393 and 21009402.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 58180 + ... + 58539.

Almost surely, 2^21009420 is an apocalyptic number.

21009420 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21009420 is an abundant number, since it is smaller than the sum of its proper divisors (42719700).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21009420 is a wasteful number, since it uses less digits than its factorization.

21009420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 116734 (or 116729 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21009420 is about 4583.6033859836. The cubic root of 21009420 is about 275.9336639567.

Adding to 21009420 its reverse (2490012), we get a palindrome (23499432).

The spelling of 21009420 in words is "twenty-one million, nine thousand, four hundred twenty".